Rhegmatogenous retinal detachment (RRD) is a potentially blinding disease that affects 1 in 10,000 people. Rhegmatogenous retinal detachments generally develop in eyes in a two-step fashion. First, excess traction on the retina from the vitreous gel inside the eye causes a retinal tear. Second, persistent traction on a retinal tear allows vitreous fluid to track underneath the retina, causing a separation of the photoreceptor layer from the underlying retinal pigment epithelium. Generally, if a rhegmatogenous retinal detachment is left untreated blindness occurs.
Myopia, or nearsightedness, is a disease in which images are focused on a point inside the eye rather than being focused on the retina. Hyperopia, or farsightedness, is a disease in which light is focused on a point behind the eye rather than on the retina. In both cases, either the focusing power of the cornea/lens combination is not appropriate for the eye length. The abnormality may lie with the size of the eye itself or may lie with the power of the cornea/lens power.
Myopia is a condition in which the power of the focusing system, e.g., cornea and lens, are too strong for the globe length, or the globe is unusually large. Hyperopia is a condition in which the eye is too short, or the power of the focusing system is too weak.
Globe size and RRD are related. Patients with enlarged eyes, i.e., myopes, are at increased risk of developing RRDs, and a number of biomechanical factors contribute to the development. Patients with hyperopia have small eyes and have a decreased risk of RRD.
Without wishing to limit the present invention to any theory or mechanism, current model of RRD implicates vitreo-retinal traction as the primary cause of retinal detachment. According to the model, vitreo-retinal traction induces a retinal tear and persistent traction causes separation of the photoreceptors from the underlying RPE cells. Vitreous fluid overwhelms the RPE pump and a RRD ensues.
The process by which retinal detachment occurs is well documented clinically and experimentally. Thompson, through his classic series of experiments on RRD, has clearly demonstrated the importance of vitreo-retinal traction in the development of RRD. Recently, data regarding the overall shapes and dimensions of eyes in emmetropia and myopia has been determined in vivo by surface coil MRI scanning. This new information can help us to understand which eyes are at greatest risk for retinal detachment and how to repair them.
Biomechanically, the insults causing a RRD may be divided into two events: the retinal tear and the actual separation of the retina from the RPE. Biomechanically, the retinal tear is no different than failure of any other structure. Failure or fracture of a structure occurs when the stress (defined as the force/cross sectional area) in the structure is high enough to overcome the inherent strength of a material.
Increased intraretinal stress can also lead to tearing of the retina. The stress can be from vitreo-retinal traction but it can also come from other sources. Intrinsic intraretinal stress depends on the retinal thickness and eye shape and is guided by Laplace's Law. LaPlace's Law essentially states that at a constant intraocular pressure, as the radius of the eye increases, the wall tension or force in the wall increases. Thus, increasing the radius of the eye increases the intraretinal stress. Thinner retinas also have increased intraretinal stress because the inherent wall tension must be carried by a smaller cross sectional area.
As we look at Atchison's MRI data regarding myopic eyes, we can understand the impact of myopic eye dimensions on intraretinal stress. Myopic globes are, in order of magnitude, longer, taller, and wider than emmetropic eyes. Myopic globes have thinner retinas horizontally but not vertically than emmetropic globes. The result of the dimensional differences is that intraretinal stress increases with increased myopia in the vertical and horizontal dimensions.
With a higher baseline intraretinal stress, less force is required to tear the retina when vitreo-retinal traction is applied. We can see why myopes have a higher risk of retinal tear when exposed to vitreo-retinal traction.
The second component in generation of retinal detachments is increased vitreoretinal traction. From Atchison's data, we know that myopic globes are, in order of magnitude longer, taller and wider than emmetropes. Although the resultant vitreo-retinal traction is difficult to quantify, we can make the following generalizations regarding the effect of globe dimensions on vitreo-retinal traction: (1) axial traction is the greatest which may be a contributing cause of early posterior vitreous detachment; (2) vertical traction is next most significant; and (3) horizontal traction is also increased, contributing to increased intraretinal stress, tearing and retinal detachments. The increased vitreoretinal traction when combined with increased intrinsic intraretinal stress and gravity makes retinal tears and RRD more likely in myopes.
The treatment of RRD may be accomplished via pars plana vitrectomy, via pneumatic retinopexy, or via a scleral buckle. In pars plana vitrectomy, three small incisions are made in the eye and the vitreous gel is dissected and removed from the eye to relieve the vitreo-retinal traction. Fluid may be drained from under the retina. The retinal tear is treated with laser photocoagulation or cryoretinopexy to induce scarring seal the hole in the retina. A gas tamponade may be used to close the retinal hole and stabilize the retina while the hole heals. In pneumatic retinopexy, a gas bubble is placed in the eye to block fluid from entering the retinal hole. The retinal tear is treated with laser photocoagulation or cryoretinopexy to induce permanent closure of the tear.
Generally, in scleral buckling, the conjunctiva and the Tenon's capsule are dissected from the sclera and a scleral buckling element (e.g.; see FIG. 1A), usually a piece of inert plastic or silicone rubber, solid or sponge, is used to indent the eye. The scleral buckle element may be sutured into place directly or may be held in place with an encircling band (imagine a belt wrapped around a volleyball). The indentation closes the hole created by the retinal tear and allows re-absorption of fluid from under the retina and resolution of the RRD. The edges of the retinal tear are treated with laser photocoagulation or cryoretinopexy to permanently seal the tear. A gas bubble may or may not be used to further seal the tear from an interior approach and subretinal fluid may or may not be removed through the sclera.
In the scleral buckle procedure, when an encircling band is used to either hold a scleral buckle in place or is used to close a hole without an additional scleral buckle element, at least one horizontal mattress suture is used in each oblique quadrant to form a belt loop in which the encircling band sits. Placement of the sutures, especially the posterior sutures, is the most difficult and risky part of the scleral buckling procedure. If the suture is not placed properly, the scleral buckle will not indent the eye at the right place, the tear will not be closed, and the retinal will not reattach. There is also risk with the placement of sclera sutures as the globe may be perforated during the suturing process. Perforation can lead to additional retinal holes and further detachment, or may result in severe hemorrhaging from the choroidal circulation with resultant scarring and possible blindness. Once the encircling band is placed around the eye, the two ends are attached to each other usually with a ring of silicone rubber. Tightening the band, like tightening a belt, decreases the circumference of the eye and causes indentation of the eye. Surgeons currently adjust tightness of the encircling band (and thus amount of indentation) manually, using experience and surgical judgment rather than any quantitated system. Knowing how much to tighten an encircling band is the second most difficult and time consuming part of the scleral buckle procedure.
Scleral buckles have a number of biomechanical effects on the eye. Specifically, a moderate height-encircling band reduces the ocular circumference and diameter, normalizes the shape of the globe (making it more round), and reverses the force vector of epiretinal membranes. The net effect is a reduction in both the intraretinal stress and vitreoretinal traction (drivers of RRD). Without wishing to limit the present invention to any theory or mechanism, it is believed that caution must be taken though in the degree of indentation because excessively high buckles increase intraretinal stress and can elevate the retina at the buckle edges. The result of excessive indentation is an increased risk in tears and redetachment. Conversely, too shallow-indentation results in an ineffective scleral buckling effect.
The present invention features novel eye shape modification (ESM) methods and systems. The eye shape modification (ESM) methods and systems of the present invention help provide modification of the globe via placement of a novel scleral buckle. Remodeling of the eye globe may help reduce biomechanical risk of retinal detachment, change refractive error, and/or prevent myopia progression. The methods and systems of the present invention may be safer and easier to surgically implant as compared to traditional scleral buckles.
Without wishing to limit the present invention to any theory or mechanism, it is believed that the methods and systems of the present invention are advantageous because the methods and systems provide the design of a calibrated system for eye shape modification (ESM), utilizes an ESM device to repair retinal detachments and reduce risk of a recurrent detachment, limits further horizontal or vertical expansion of the eye in myopia, and lengthens the eye in hyperopia.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.